Waveguide

ABSTRACT

A waveguide structure including two parallels electrically conducting ground planes ( 1,2 ), each of which includes at least one row of spaced apart electrically conducting posts ( 3 ). The rows of posts are arranged substantially parallel to one another and the space bounded by the plates and posts defines a guided wave region ( 4 ) along which electromagnetic radiation may propagate. The posts are connected to only one of the planes so that there is no physical connection between the two ground planes ( 1,2 ). Actuating means may be connected to one or both of the ground planes to cause relative movement there between to thereby alter the electrical response of the waveguide. The direction of the relative movement may such that the distance between the rows of posts ( 3 ) is changed and/or the distance between the ground planes ( 1,2 ) is changed. Various device may utilize the described waveguide construction, including reconfigurable waveguide filters and antenna structures e.g. slotted waveguide arrays.

INTRODUCTION

This invention relates to waveguides and in particular, though notsolely, to waveguides which include mechanically movable parts to altertheir electrical characteristics.

Transmission lines,. and in particular waveguides, have manyapplications in the microwave field including radiofrequencybeamformers, filters, rotary joints and phase shifters. The use of lowcost manufacturing techniques, including the use of metallised plasticsfor the implementation of multilevel beamforming architectures have beendescribed in, for example, EP-A-1148583. Such structures generallyrequire that the metallised plastics waveguide parts are slit, ideallyalong the centre of the broadwall (E-plane) in the case of rectangularwaveguides.

However, it is very well known that slits in the narrow walls ofrectangular waveguides lead to high attenuation due to the largecurrents flowing across the slit discontinuity.

Such split constructions allow multilevel beamformers to be realised byfabrication of individual parts that are subsequently bonded together insuch a way that the impact of the joint is minimised. In the case ofmetallic waveguides this sometimes involves dip brazing, or in the caseof metallised plastics, limits the joint's position along the centre ofthe broadwall, in the case of rectangular waveguides. Such restrictionsdo not apply to dip brazed components, however these are not well suitedto volume manufacture.

Waveguide devices with moving parts (for example, rotary joints forradar antennas, phased arrays, radio frequency switches, reconfigurablefilters and phase shifters) are difficult to implement since waveguidesare usually based on closed metal cavities. There is therefore aconstraint imposed on the implementation of mechanically actuated phaseshifting devices based on waveguides because metal or dielectric parts,including the actuator, have to be mounted inside the waveguide therebyintroducing losses and distortion and requiring-a relatively complexdesign. An example of a mechanically actuated phase shifting device isdisclosed in FR-A-2581255.

Controlled phase shifting using electronic components such as ferritephase shifters and electronic switches (i.e. PIN diodes) have beendeveloped over the last 30 years and these have found extensiveapplication in radar and radio location systems, as a way of steering orreconfiguring antenna radiation patterns.

A major obstacle to the use of electrically controlled phase shifters inmany scanning beam antenna applications is the high cost and the largenumber of phase shifting devices required for beam steering. Theproduction cost of electronically scanned antennas is still very high,even when significant volumes are produced. In addition, electronicphase shifters introduce additional losses and a considerable DC powerconsumption that limits their application for systems that use batteriesfor power supply such as mobile/personal communication devices.

Mechanical phase shifters are an attractive low cost solution forantenna applications that do not require a fast (in the order ofmilliseconds) scan of the beam. Mobile satellite communication links onstable platforms like cars, ships and commercial aircraft require scanrates in the order of only tenths of a second, which can be achieved bymechanical means.

A number of mechanical phase shifters have been developed in recentyears. Most of them, such as EP-A-1033773 and U.S. Pat. No. 5,504,466are based on the variation of the physical dimensions (including length)of a waveguide or transmission line. Others, such as EP-A-0984509 andU.S. Pat. No. 5,940,030, are based on movable dielectric elements insideor close to transmission lines. Another approach is based on a periodicspatial loading of transmission lines and is described in EP-A-1235296wherein the amount of electrical loading on the line caused by theperiodic structure is controlled using a moving metal plate in thevicinity of the periodic structure on the line.

Most of these devices are simple to manufacture, have reasonably lowlosses and are easily implemented at a low frequency band (typicallyL-Band and S-band) for coaxial lines and for other TEM lines such asstripline and microstrip. The implementation of these electromechanicaltechniques for high frequencies (typically Ku-Band, Ka-Band andmillimetre wavelengths) in waveguide structures is much more difficult;in particular because high frequency waveguides are formed by a solidmetal enclosure which becomes lossy when filled with dielectrics.

One possible way to realise an electro-mechanical phase shifter is touse a secondary movable wall inside a metal waveguide as disclosed inU.S. Pat. No. 3,789,330, however, this approach is difficult to realisesince the secondary wall cannot be connected to the waveguide if it isto be freely movable. This can result in the generation of spurious andadditional waveguide modes which are very difficult to control. Anotherissue is the placement of the control device. If the device is placedinside the waveguide (i.e a piezoelectric crystal), it can producesevere distortion of the waveguide modes and introduce large losses. Ifthe device is outside the waveguide, such as for example in theabovementioned FR-A-2581255, the metal enclosure must be perforated toallow access to the moving part thereby introducing additionaldistortion and losses.

The combination of mechanical antenna rotation with single planescanning using phase shifters was described in “An Array-fed DualReflector Antennas for Limited Sector Beam Scanning”, R A Pearson, PhDThesis, University of London, April 1988, in which equi-spaced array ofwaveguide radiators is filled using flares along the length of the phasescanning plane, the whole structure being rotated to scan the beam inany arbitrary plane. In that implementation the primary radiatingstructure was further combined with a dual reflector system to magnifythe aperture.

Alternative waveguide configurations using periodic structures known asPhotonic Band Gap (PBG) crystals, have been suggested in the last decade(see for example “Photonic Crystals: Molding the flow of light”, J Djoannopoulos, Princeton University Press, NJ 1995) to simplify themanufacture of dielectric waveguides, especially at the infrared andvisible light region of the spectrum. Most of these waveguides are basedon fixed periodic distributions of dielectric materials acting asboundaries for the guided electromagnetic wave. Practical applicationsof these techniques to radio frequencies are much less developedalthough examples are shown in “A Novel waveguide using UniplanarCompact Photonic Bandgap (UC PBG) Structure”, IEEE Transactions onMicrowave Theory and Techniques, Vol 47, No. 11, November 1999 and ourEuropean Patent Application No. EP01304526.5. Despite its potential,these waveguide configurations using periodic structures do not overcomethe manufacturing problems associated with contact between movingwaveguide parts and they do. not allow moving parts within the structureto implement mechanical phase shifters, rotary joints and otherreconfigurable devices for radio circuits.

It is therefore an object of the present invention to provide awaveguide which goes at least some way towards. overcoming the abovedisadvantages or which will at least provide the industry with-a usefulchoice.

SUMMARY OF THE INVENTION

In a first aspect, the invention consists in a waveguide comprising:

a first electrically conductive ground plane,

a second electrically conductive ground plane spaced from and parallelto the first ground plane,

a first row of electrically conductive spaced posts fixed to andextending substantially perpendicularly from the first ground planetowards but not touching the second ground plane,

a second row of electrically conductive spaced posts fixed to andextending substantially perpendicularly from the second ground planetowards but not touching the second ground plane,

the volume bounded by the first and second ground planes and the firstand second rows of posts defining a guided wave region along whichelectromagnetic radiation may propagate.

Preferably, the first and second rows of posts are parallel so that theguided wave region has a substantially constant cross-section.

Preferably, the posts of the first and second rows are all of the samelength which is less than the distance between the first and secondground planes.

Preferably, the distance between the first and second ground planes isabout half a wavelength at the operating frequency and the posts have alength of about one quarter of a wavelength.

Preferably, the width of the posts is about ⅓ of the post height.

Preferably, one of the first or second ground planes includes acontinuous step, between and parallel to the first and second rows ofposts.

Preferably, actuating means are connected to one or both of the groundplanes to provide relative movement between the rows of posts by movingthe first and second ground planes relative to each other to therebyadjust the propagation constant of the guided electromagnetic wave.

Preferably the distance between the first and second rows of posts ischanged but the distance between the ground planes is unchanged by therelative movement.

Alternatively, the distance between the ground planes is changed but thedistance between the first and second rows of posts is unchanged by therelative movement.

Preferably, the first ground plane is provided with a plurality ofparallel spaced apart first rows of posts and the second ground plane isprovided with a plurality of parallel spaced apart second rows of posts.

In a second aspect, the invention consists in a passive reconfigurablefilter including a waveguide according to the first aspect, and

actuating means connected to one or both of the ground planes to providerelative movement between the rows of posts by moving the first andsecond ground planes relative to each other to thereby adjust thefrequency response of the waveguide.

In a third aspect, the invention consists in a phase shifting deviceincluding a waveguide according to the first aspect, two transitionsconnecting fixed solid waveguides at the input and output of the deviceto the waveguide according to the first aspect, and actuating means toprovide relative movement between rows of posts to thereby adjust thepropagation constant of the waveguide.

In a fourth aspect, the invention consists in an array of parallelaligned waveguides according to the first aspect, each of the waveguidessharing common first and second ground planes.

In a fifth aspect, the invention consists in a beam scanning antennaarray comprising an array of parallel aligned waveguides according tothe third aspect, each waveguide having at least one radiating slot, theslots from all of the waveguides provided in only one of the first orsecond ground planes and each slot aligned with or perpendicular to thepropagation direction of the guided wave region, and

actuating means connected to one or both of the common ground planes toprovide relative movement between the rows of posts by moving the firstand second ground planes relative to each other to thereby steer theantenna beam in the elevational plane of the antenna array.

Preferably, rotating means are provided to rotate the scanning antennaarray in a plane perpendicular to the elevational plane.

Preferably, a periodic structure is also provided within each waveguideto delay the guided electromagnetic wave and thereby extend the angularscanning range of the antenna beam.

Preferably, an array of radial horns or dielectric lenses are alsoprovided, each radial horn or dielectric lense juxtaposed adjacent theat least one radiating slot of respective waveguides.

Preferably, at least one of the top or bottom ground planes is formedfrom a dielectric plate, the posts formed integrally therewith, theposts and only the surface of the dielectric plate facing the otherground plane coated in a conductive material, wherein the radiatingslots are formed in the metal coating, and wherein the dielectric lensesare integrally formed with the dielectric plate.

Accordingly, the waveguide may have two parallel metallic plates and aperiodic structure of metal posts connected to one or other of theplates, without simultaneous physical contact to both. At somefrequencies, the periodic structure creates a virtual short circuitbetween the parallel plates, preventing the leakage of energy from thewaveguide. Structures including waveguides, beamformers and rotary orrotating joints can be built utilising the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular examples of the invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a rectangular waveguide structure inaccordance with the present invention;

FIG. 2 is a cross-sectional view through the line 2-2 of the rectangularwaveguide of FIG. 1;

FIG. 3 is a perspective view of a ridge waveguide made in accordancewith the present invention;

FIG. 4 is a scanning array of radiating slots on waveguides according tothe present invention;

FIG. 5 is a perspective view of a phase shifting device including awaveguide in accordance with the present invention, two transitions andtwo fixed solid waveguides; and

FIG. 6 is a perspective view of a scanning array of radiating slots onwaveguides according to the present invention having mobile dielectricsupports.

DESCRIPTION OF PARTICULAR EMBODIMENT

With reference to the drawings and in particular FIGS. 1 and 2, awaveguide is shown which includes two electrically conductive platesforming top 1 and bottom 2 ground planes. The ground planes 1,2 arearranged substantially parallel to each other and separated by a seriesof conductive posts 3. The conductive posts 3 are arranged substantiallyperpendicular to both of the ground planes 1,2. Ground planes 1,2 andposts 3 may, for example, be metallic or may be made from a metallisedplastics material.

The posts 3 are typically distributed periodically in straight lines inone or more rows on either side of a central, guided wave region 4 whichis free of posts and in which electromagnetic energy is guided andconfined. The spacing of adjacent posts in a row is not necessarilyconstant, the distance between adjacent parallel rows is not necessarilythe same and the spacing of posts in different rows is also notnecessarily the same. However, it is preferred that the posts areuniformly spaced in each row and that the spacing is constant in allrows. Preferably the spacing between adjacent rows is about λ/10 and thespacing between posts in the same row is less than about λ/4 where λ isthe wavelength at the central frequency of the operating band.

Each conductive post 3 is connected at only one of its ends to eitherone of the ground planes, leaving a gap 5 between each post 3 and theopposing ground plane 1 or 2. The waveguide construction may thereforebe considered “contact-less” because the top 1 and bottom 2 groundplanes are effectively not connected by conventional side walls. Theposts 3 may be bonded or welded to their associated ground plane or maybe integral therewith.

Each of the posts 3 on one side of the guided wave region 4 areconnected to the top ground plane 1 while each of the posts 3 on theother side of the guided wave region 4 are connected to the bottomground plane 2. As the posts 3 are in straight rows and areperpendicular to the ground planes 1,2, the shape of the central guidedwave region 4 is substantially rectangular as shown in FIG. 2 with awidth w as shown in FIG. 1. In the working frequency band a virtualshort circuit (zero impedance) is created between the top 1 and bottom 2ground planes by resonance of the posts associated inductance andcapacitance. A guided wave will therefore propagate in the guided waveregion 4 in the direction parallel to the rows of posts 3 as shown byarrow 6 in FIG. 2.

In the operating frequency band, the separation between parallel platesis less than half a wavelength, more preferably between about 0.3λ andabout 0.4λ. The height of the posts 3 is of the order of one quarter ofthe wavelength at the central frequency of the operating band and morepreferably between about 0.2λ and about 0.3λ, but the post height alsodepends on the post diameter and the separation between them due tomutual coupling between adjacent posts. The cross-sectional shape of theposts may be, for example, rectangular (including square), circular orelliptical and may be selected based upon the manufacturing procedureused. Other cross-sectional shapes are also possible if they areconvenient for manufacturing and so long as they have sufficientassociated inductance and capacitance for resonance to occur within auseful frequency range. The diameter of the posts is much smaller thanthe height and may, for example, be less than or equal to about ⅓ of thepost height.

As previously mentioned, the conductive posts 3 create a virtualconductive wall or virtual short circuit in the operating frequencyband. In fact, the posts 3 behave as an equivalent resonant circuit inparallel with the ground plane 1,2. A row of posts 3 produces a lowimpedance boundary, similar to a metallic wall connecting the top 1 andbottom 2 planes thereby effectively simulating the function of planarside walls in conventional rectangular waveguides. The combination ofseveral rows of posts 3 can be used to extend the bandwidth of thewaveguide as compared to the case of the virtual walls formed by singlerows of posts 3.

For a rectangular shaped contact-less waveguide, the fundamentalelectromagnetic mode inside the waveguide is very similar (outside thepost areas) to the TE₁₀ mode of a conventional rectangular waveguidehaving an equivalent width approximately equal (typically 1-2% less) tothe width w of the central guided wave region 4 of the contact-lesswaveguide.

As the top 1 and bottom 2 ground planes are not physically connected, itis possible to displace one with respect to the other by moving one orboth of the ground planes 1,2 (and thereby the rows of posts 3) in thedirection of arrows 7 and 8 in FIG. 1. This relative movement alters thewidth of the guided wave region 4. This produces a modification to thewaveguide impedance and wave propagation constant and therefore can beused to reconfigure the electric performance of a waveguide or a deviceor circuit based on the waveguide according to the present invention.

The dimensions of the waveguide can thus be changed, without the use ofadditional internal dielectric or metallic parts, which could interferewith the fields inside the waveguide, to create a phase change along thewaveguide. The waveguide according to the invention is therefore capableof acting as a phase shifter. If one of the ground planes 1,2 isdisplaced laterally with respect to the other, the virtual short circuitwall is also displaced, keeping the basic rectangular shape of thewaveguide unchanged. The phase of the wave at the end of the waveguideis modified since the propagation constant of the wave inside thewaveguide is directly related to the width w of the waveguide. Thepropagation constant of the fundamental mode of the waveguide can becalculated using the formula:$\gamma = \sqrt{k^{2} - \left( \frac{\phi_{11}}{w} \right)^{2}}$where k is a constant, w is the width of the channel between the innerrow of posts 3 and φ₁₁, is the phase in radians of the reflectioncoefficient of the posts 3 to an incident TEM parallel plane wave. Ingeneral, φ₁₁ depends on the frequency and the angle of incidence, whichis directly related to the propagation constant γ.

Relative vertical displacements of the ground planes 1,2 can also beused to introduce phase shift for a contact-less version of thewaveguide and in particular to a contact-less version of a ridgewaveguide as shown in FIG. 3. In FIG. 3, the posts 3 (shown havingsquare cross-sections in this example) and a conductive ridge 9, whichextends parallel to the rows of posts, could all be attached to the sameground plane 1,2. Alternatively, the posts 3 on one side of the centralguided wave region 4 and the ridge 9 could be connected to the sameground plane 1,2 and the posts 3 on the other side of the central guidedwave region 4 could be connected to the other ground plane 2,1.

The distance between ridge 9 which is attached to top ground plane 1 inthe example shown and the opposing bottom ground plane 2 greatlyinfluences the propagation constant. In this case, the maximum allowablerelative displacement between the ground planes is limited by theallowable gap g between the posts 3 and the respective opposing plates1,2. It will be appreciated that if the gap g exceeds a threshold valuethen the posts 3 may stop acting as virtual walls and the response ofthe waveguide will be effected.

Well known linear transducers or electric motors could be suitablyconnected to the outer surface of one or both of the ground planes 1,2in order to accomplish the required relative movement in the lateral orvertical directions. Lateral and vertical displacement could beincorporated in the design of a single waveguide.

Contact-less waveguides can be used to implement power dividers,filters, couplers and other passive devices typically used in radio ormicrowave networks. The electrical characteristics of these devices canalso be changed by the relative displacement of the top 1 and bottom 2ground planes and their associated posts 3.

It is also possible to realise structures that utilise the contact-lessaspect of the invention to implement mechanical displacement, forexample to steer the beam transmitted and/or received by an integral orseparate radiating structure, or as part of a rotary joint, in which theelectrically significant parts are physically separated and parts whichare not critical electrically are used to realise the mechanicalrotation. Reconfigurable waveguide filters can also be implemented usingthe contact-less waveguide since the width of resonating sections of thewaveguide can be changed by lateral displacement thereby effecting thewaveguide's frequency response.

It is possible to simultaneously control phase changes in severalassociated waveguides which share the same ground planes 1,2. Thewaveguides may have different widths w and operate at differentfrequencies, but they must have the same height since the separationbetween ground planes 1,2 is the same for all of them.

Contact-less waveguides according to this invention can also radiate orabsorb electromagnetic waves and therefore act as antennae by controlledleakage or absorption of energy from apertures in one or both groundplanes 1,2. The radiation/absorption from these apertures depends ontheir relative position and orientation in the ground planes, in asimilar way to the apertures in conventional rectangular waveguides.

Due to the similarity between the fields in the present contact-less andconventional rectangular waveguides, it is possible to implementcontact-less versions of conventional slotted waveguide arrays and ofconventional radiators using a longitudinal slot utilising the waveguideaccording to this invention.

FIG. 4 shows an example of a scanning array of radiating slots (tworadiating slots 10,11 in the top ground plane 1 are shown) oncontact-less waveguides according to this invention. The propagationconstant of slotted waveguides according to this invention can becontrolled simultaneously by a single lateral displacement betweencommon ground planes 1,2 in the direction of arrow 12. In FIG. 4, onlytwo waveguides 13,14 are shown, both sharing common top 1 and bottom 2ground planes with respective virtual side walls formed by rows ofconductive posts 3. The rows of posts 15 and 16 form virtual side wallsfor waveguide 13 while rows of posts 17 and 18 form virtual side wallsfor waveguide 14. The posts 3 in rows 15 and 17 should be connected toonly one, but the same, ground plane 1 or 2 while the posts in rows 16and 18 should be connected to only one, but the other, ground plane 2 or1.

In order to improve the radiation efficiency of the slots, an array ofradial horns or an array of dielectric lenses may be positioned adjacentthe top ground plane 1, each of the horns or lenses aligned with arespective radiating slot. In the case of dielectric lenses being added,the array of lenses, slots and posts may be constructed integrally witheach other and one of the ground planes. This may be accomplished byconstructing one of the ground planes (for example, top ground plane 1)using metallised plastics wherein a plate of plastics material is usedto form a single solid dielectric lens array layer which is coated withmetal on one side (the other, outer side, need not be metallised) toform the top ground plane which faces the bottom ground plane 2. Slots10,11 etc are etched in the metal layer and posts are moulded or formedintegrally with the plastics plate, on the same side as the etchedmetallised ground plane, and also metallised. This construction providesa robust mechanical structure. The slots 10, 11 may have a slot widthwhich may be varied periodically. The slots 10, 11 may also be coveredwith a thin layer of dielectric material to prevent the radiation ofslotline waves.

Each radial horn aperture or dielectric lens structure may be providedwith an integral polarising structure to, for example, generatecircularly polarised waves on transmit or to convert a circularlypolarised wave to linear polarisation to thereby provide efficientcoupling to the on receive.

The direction of the radiation beam generated (or received) by thesearrays is directly related to the propagation constant inside thewaveguide. As a result, the antenna beam is steered in the elevationplane by the relative displacement of the ground planes 1,2. Atmicrowave frequencies (Ku-Band and Ka-Band) the lateral displacementrequired to scan a beam from 30° to 60° is in the order of severalmillimetres, and can be realised by means of, for example, conventionallow cost electrical motors.

Corrugations or a similar periodic conductive or dielectric structuremay either be positioned inside the waveguides or may form an integralpart of the inner conducting surface of the upper 1 or lower groundplane. The periodic structure delays or slows down the electromagneticwave within the wave guide and, therefore, in conjunction with thewaveguide according to his invention, extends the angular scanning rangeof the antenna scanning beam.

Antenna structures particularly suited to circular polarisation cantherefore be made using this invention, with beam scanning along thelength of the waveguide, to thereby realise full beam scanning as partof a low profile structure by rotating the whole structure orthogonal tothe plane of the antenna aperture.

The scanning array may further be provided with mobile dielectricsupports 23 between the first and second ground planes 1, 2 withincavities formed by rows of posts 15, 16, 17, 18 in order to ensure themechanical stability of the array without hampering the movement of theground planes 1,2.

FIG. 5 shows an example of a phase shifting device including two fixed,solid waveguides 19, 22 and a waveguide in accordance with the presentinvention. One of the fixed, solid waveguides 19 is disposed at theinput of the phase shifting device and is connected to the waveguide viaa transition 20. The other of the fixed, solid waveguides 22 is disposedat the output of the phase shifting device and is connected to thewaveguide via another transition 21. Actuating means may be connected toone or both of the ground planes 1, 2 of the waveguide to providerelative movement between rows of posts to thereby adjust thepropagation constant of the waveguide. Accordingly, controlled phaseshifting may be performed.

1. A waveguide comprising: a first electrically conductive ground plane,a second electrically conductive ground plane spaced from and parallelto the first ground plane, a first row of electrically conductive spacedposts fixed to and extending substantially perpendicularly from thefirst ground plane towards but not touching the second ground plane, asecond row of electrically conductive spaced posts fixed to andextending substantially perpendicularly from the second ground planetowards but not touching the first ground plane, the volume bounded bythe first and second ground planes and the first and second rows ofposts defining a guided wave region along which electromagneticradiation may propagate.
 2. The waveguide of claim 1, wherein the firstand second rows of posts are parallel so that the guided wave region hasa substantially constant cross-section.
 3. The waveguide of claim 1,wherein the posts of the first and second rows are all of the samelength which is less than the distance between the first and secondground planes.
 4. The waveguide of claim 1, wherein, the distancebetween the first and second ground planes is about half a wavelength atthe operating frequency and the posts have a length of about one quarterof a wavelength.
 5. The waveguide of claim 1, wherein the width of theposts is about ⅓ of the post height.
 6. The waveguide of claim 1,wherein one of the first or second ground includes a continuous step,between and parallel to the first and second rows of posts.
 7. Thewaveguide of claim 1 wherein actuating means are connected to one orboth of the ground planes to provide relative movement between the rowsof posts by moving the first and second ground planes relative to eachother to thereby adjust the propagation constant of the guidedelectromagnetic radiation.
 8. The waveguide according to claim 7,wherein the distance between the first and second rows of posts ischanged but the distance between the ground planes is unchanged by therelative movement.
 9. The waveguide according to claim 7, wherein thedistance between the ground planes is changed but the distance betweenthe first and second rows of posts is unchanged by the relativemovement.
 10. The waveguide according to claim 1 wherein the firstground plane is provided with a plurality of parallel spaced apart firstrows of posts and the second ground plane is provided with a pluralityof parallel spaced apart second rows of posts.
 11. A passivereconfigurable filter including a waveguide according to claim 7,wherein relative movement of the-first and second ground planes adjuststhe frequency response of the waveguide.
 12. A phase shifting deviceincluding a waveguide according to claim 7, and two transitionsconnecting two solid waveguides to the waveguide, wherein relativemovement of the first and second ground planes adjusts the propagationconstant of the waveguide.
 13. An array of parallel aligned waveguidesaccording to claim 1, wherein each of the waveguides share common firstand second ground planes.
 14. A beam scanning antenna array comprising:an array of parallel aligned waveguides according to claim 13, eachwaveguide having at least one radiating slot, the slots from all of thewaveguides provided in only one of the first or second ground planes andeach slot aligned with or perpendicular to the propagation direction ofthe guided wave region, and actuating means connected to one or both ofthe common ground planes to provide relative movement between the rowsof posts by moving the first and second ground planes relative to eachother to thereby steer the antenna beam in the elevational plane of theantenna array.
 15. A beam scanning antenna array as claimed in claim 14,further comprising rotating means provided to rotate the scanningantenna array in a plane perpendicular to the elevational plane.
 16. Abeam scanning antenna array as claimed in claim 14 wherein a slot widthis defined as the lesser slot dimension, the slot width being variedperiodically, or wherein the slot is covered with a thin layer ofdielectric to prevent the radiation of slotline waves.
 17. A beamscanning antenna array as claimed in claim 14, further comprising aperiodic structure within each waveguide to delay the guidedelectromagnetic wave and thereby extend the angular scanning range ofthe antenna beam.
 18. A beam scanning antenna array as claimed in claim14, further comprising an array of radial horns or dielectric lenses,each radial horn or dielectric lense juxtaposed adjacent the at leastone radiating of respective waveguides.
 19. A beam scanning antennaarray as claimed in claim 18, wherein at least one of the top or bottomground planes is formed from a dielectric plate, the posts formedintegrally therewith, the posts and only the surface of the dielectricplate facing the other ground plane coated in a conductive material,wherein the radiating slots are formed in the metal coating, and whereinthe dielectric lenses are integrally formed with the dielectric plate.20. A beam scanning antenna array as claimed in claim 14, furthercomprising mobile dielectric supports between the first and secondground planes within cavities formed by the rows of posts in order toensure the mechanical stability of the array without hampering themovement of the ground planes.